1. Field of the Invention
The present invention relates to an apparatus and method for sealing a liquid sump. More specifically, the present invention relates to seal ring segments designed to generate high gas pressures across the seal and around a rotating shaft so as to prevent liquids from leaking from a liquid side of the seal to a gas side of the seal during low and high pressure conditions.
2. Background
There are many applications wherein housings are provided with a plurality of interior sections having rotating parts passing therethrough, wherein one of the interior housing sections must be isolated from another by means of a seal system. In gas turbine applications, for example, it is critical that lubricant contained within a lubricant chamber of the housing be sealed from an adjacent gas side of the seal. This is especially true along a rotatable shaft which often passes from the lubricant side of the seal to the gas side. In an aircraft engine these sump seals are used to separate ambient areas of high pressure air, e.g. the gas side, from an oil wetted area at lower ambient pressures, e.g. the lubricant side. These seals, thereby, serve two major functions: (1) prevention of oil leakage from the lower pressure compartment, and (2) minimization of the flow rate of hot air from the high pressure area to the oil wetted compartment.
Leakage of liquids from the lubricant side into the gas side adversely affects performance of the equipment where the seal is used. In case of an aircraft engine, oil leakage across the seal into a hot air side may cause oil coking or an engine fire. More specifically, when an oil lubricant is used, mixing the oil with the gas could result in formation of oil coke, a byproduct of oil heated to an elevated temperature, which chemically alters the oil and is detrimental to the gas turbine. Oil coke can foul seal surfaces reducing the integrity of the seal and prevent proper bearing lubrication within the lubricant sump. Accordingly, it is important in similar applications, not just the aircraft engine, that the lubricant be isolated within a lubricant sump and that the seal around the rotating shaft not allow the lubricant to escape the sump.
Seals in such applications may comprise either circumferential seals or face-type seals; however, the circumferential shaft seals are the most widely used under the above conditions. Circumferential seal is a name describing a generic type of seating device used widely, inter alia, on aircraft engine applications. FIGS. 1A and 1B show a liquid side 2 and a gas side 3 of a standard circumferential seal assembly 1. FIGS. 2A and 2B show back face and bore views of the same standard circumferential seal ring segment. In each of these figures, the seals consist primarily of several carbon and/or graphite segments 1 arranged circumferentially around a shaft 5 to form a continuous, relatively stationary sealing ring. The segment ends contain overlapping tongue 10 and socket joints 15 to restrict leakage at the end gaps of each segment.
Most current circumferential seals utilize a variant of the circumferential seal illustrated in FIGS. 1 and 2 to address a need for sealing a low pressure liquid compartment from such a high pressure gas compartment. For example, U.S. Pat. No. 5,145,189 discloses a similar circumferential seal with a shallow groove which redirects pressurized air to a plurality of deeper vent grooves. U.S. Pat. No. 6,145,843 also discloses a similar circumferential seal with shallow lift pockets in fluid communication with a high pressure region by a plenum chamber. Both of these solutions rely completely on the high pressure differential between the lubricant side and the gas side to achieve each respective sealing function. To this end, in low gas pressure conditions, anywhere from 5 psi and below and including negative pressures, these known circumferential seals can weep, namely, leak liquids from the liquid side into the gas side. Liquid leaking, as noted above, increases the risk of oil coking and fouling the seal face. This increases the risk of engine fire and increases the risk of oil odor within a vehicle housing the engine.
Accordingly, a seal is desired which may function to prevent liquid or oil leaking from a liquid or oil side to a gas side of an application, such as a turbine engine, wherein the seal may prevent leaking under low pressure differentials between a lubricant side and a gas side, as well as, high pressure differentials. The present invention, as disclosed herein, addresses this need.